Viscous Drag and Turbulence Reduction for Wind Turbine Blades, Submarines, Pipeline Flow Using Bio-Inspired Fibrillar Structures

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mushroom-shaped fibrillar structures for drag reductionairfoil with micro-fibers being tested in wind tunnelairfoil fabrication by nanoGrip for testing
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Researchers
Luciano Castillo, PhD.
Don Kay and Clay Cash Foundation Engineering Chair in Wind Energy and Mechanical Engineering professor
External Link (www.depts.ttu.edu)
Burak Aksak, PhD.
Assistant professor, Mechanical Engineering
External Link (www.depts.ttu.edu)
Managed By
Cameron Smith
Licensing Associate 806-834-6822
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Provisional Patent Application Filed

PCT Patent Application Filed
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WO2014165106.pdf [PDF]

These bio-inspired fibrillar structures reduce viscous drag and turbulence on surfaces of wind turbine blades, the hulls of submarines, and the interior of oil pipelines by up to 40 percent. Reducing drag and turbulence reduces their power consumption by improving machine speed and endurance.

These mushroom-shaped fibers — inspired by gecko footpads and lotus leaves — add a controlled, periodic roughness to wind turbine blade, submarine or pipeline surfaces, creating pockets of air between fibers to produce a slip velocity that reduces viscous drag.

The micro-fiber structures are made from a simple micro-molding process and use readily available, low-cost, commercial materials like silicon rubber and polyurethane plastics. Any moldable material is compatible with the manufacturing process, allowing for a wide material selection. This flexibility in materials and easy, large-scale production make this technology commercially marketable.

 In wind tunnel tests, reduced drag by 40 percent and increased lift by 113 percent — the the highest levels obtained by passive systems used for drag reduction, far surpassing a micro-groove technology called riblets that achieved only a 10 percent reduction in drag.  

Fibrillar Structures are Customizable and Tunable for Optimal Performance

The fibrillar structures are made from polymers using photolithography and micro-molding. The fibers can be customized for any surface; the fabrication technique allows control of the diameter, length, cross-sections, and packing of fiber density. It is possible to control the alignment of the stalk and tip separately, which helps create surfaces with anisotropic, or multi-directional, drag properties. Moreover, it is possible to create fiber arrays with heterogeneous fiber geometry, so that individual fibers forming the arrays have varying cross-sectional shape, diameter, and spacing. This tuning ability provides optimal performance for transitional flows.  

Applications

  • Wind turbine blades for the wind energy industry
  • Submarines or other underwater bodies, civilian or military
  • Wing design for the aerospace industry
  • Pipe flow turbulence reduction for petroleum industry, water and sewer departments
  • Turbulence and drag reduction research

Advantages

  • Low manufacturing costs relative to other drag reduction technologies
  • Fibrillar structures can be constructed using a wide variety of readily available materials, making the technology customizable and controlling material costs
  • Polymer microfilm with desired fibrillar structures can be manufactured for large-scale applications like submarines or aeroplanes 
  • Tested highest drag reduction and lift enhancement of any passive drag reduction system, offering significant improvement in speed and efficient, reducing power consumption
  • Reduced carbon footprint for military and civilian transportation from improved speed and reduced power consumption
  • Faster, more efficient delivery of materials such as oil, medicine, and troop supplies

About the Researchers

Dr. Luciano Castillo is a Don Kay and Clay Cash Foundation Engineering Chair in Wind Energy and a professor in the Mechanical Engineering department. His areas of expertise are modeling and experimental wind energy array, single−blade aerodynamics for turbine blades, multi−scale and asymptotic methods in turbulent boundary layers, experimental, theoretical, and numerical fluid mechanics, and forced convection heat transfer.

Dr. Burak Aksak is an assistant professor in the Mechanical Engineering department. His research interests include development of bio−inspired devices for adhesion, sensing, actuation and energy harvesting and multi−functional, self−sufficient systems which exploit the increased surface−to−volume ratio and the high sensitivity of micro/nano structures.